A laminated glass is a safety glass because few glass fragments are scattered even if it is broken by impact from the outside. Therefore, laminated glasses have been widely used for windowpanes or the like of vehicles such as automobiles, aircrafts, and buildings. An example of those laminated glasses is a laminated glass produced by interposing an interlayer film for a laminated glass including, as a binder resin, a polyvinyl acetal plasticized by a plasticizer between at least a pair of glass plates, and then laminating and integrating the glass plates and the interlayer film.
The wavelength range of infrared rays is 780 nm or longer, which is in long-wavelength side as compared to the wavelength range of visible lights. The amount of energy of infrared rays is approximately 10% of that of ultraviolet rays. When absorbed in a material, infrared rays are converted into heat and then emitted so that the surrounding temperature is increased. For example, by shielding infrared rays which pass through a windshield or a side window glass of an automobile, the temperature inside the automobile can be prevented from increasing. Since there is a trend that automobiles and the like have larger openings these days, a laminated glass with a reduced infrared ray transmissivity has been demanded.
Patent Document 1 discloses an interlayer film for a laminated glass having an improved infrared ray-shielding performance due to lanthanum hexaboride particles dispersed therein. Since lanthanum hexaboride particles have a high infrared ray-shielding performance, dispersion of even a little amount of lanthanum hexaboride particles in the interlayer film for a laminated glass makes it possible for the interlayer film to achieve a high infrared ray-shielding rate.
In-vehicle devices controllable using infrared communication waves have been developed these days. A rain sensor, for example, detects the presence of raindrops by having infrared rays of about 850 nm wavelength reflected on the raindrops on the windshield. For the control or the like of the in-vehicle device, near-infrared rays having a wavelength of about 800 to 1000 nm are used.
Lanthanum hexaboride particles shield infrared rays having a wavelength shorter than 1500 nm, and notably near-infrared rays having a wavelength of about 800 to 1000 nm. Therefore, when an interlayer film for a laminated glass containing lanthanum hexaboride particles is used, the infrared communication waves do not pass through the film, problematically making it impossible to use the in-vehicle device.
Patent Document 2 discloses an interlayer film for a laminated glass which allows infrared communication waves to be transmitted from outside to inside, or vice versa, of a vehicle by providing an infrared ray-transmittable region which practically does not include infrared ray-shielding particles.
When such an infrared ray-transmittable region is provided, even though infrared communication waves pass through the region, the infrared ray-shielding performance of the windshield as a whole is significantly decreased. Accordingly, it is problematically impossible to prevent the temperature inside a vehicle from increasing.
Patent Document 1: Japanese Kokai Publication 2001-89202 (JP-A 2001-89202)
Patent Document 2: Japanese Kokai Publication 2002-173347 (JP-A 2002-173347)